Biochar is a carbon-rich coproduct resulting from pyrolyzing biomass. When applied to the soil it resists decomposition, effectively sequestering the applied carbon and mitigating anthropogenic CO2 emissions. Other promoted benefits of biochar application to soil include increased plant productivity and reduced nutrient leaching. However, the effects of biochar are variable and it remains unclear if recent enthusiasm can be justified. We evaluate ecosystem responses to biochar application with a meta-analysis of 371 independent studies culled from 114 published manuscripts. We find that despite variability introduced by soil and climate, the addition of biochar to soils resulted, on average, in increased aboveground productivity, crop yield, soil microbial biomass, rhizobia nodulation, plant K tissue concentration, soil phosphorus (P), soil potassium (K), total soil nitrogen (N), and total soil carbon (C) compared with control conditions. Soil pH also tended to increase, becoming less acidic, following the addition of biochar. Variables that showed no significant mean response to biochar included belowground productivity, the ratio of aboveground : belowground biomass, mycorrhizal colonization of roots, plant tissue N, and soil P concentration, and soil inorganic N. Additional analyses found no detectable relationship between the amount of biochar added and aboveground productivity. Our results provide the first quantitative review of the effects of biochar on multiple ecosystem functions and the central tendencies suggest that biochar holds promise in being a win-win-win solution to energy, carbon storage, and ecosystem function. However, biochar's impacts on a fourth component, the downstream nontarget environments, remain unknown and present a critical research gap.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/gcbb.12037

Biochar and its effects on plant productivity and nutrient cycling: a meta‐analysis

Physico-chemical properties and microbial responses in biochar-amended soils: Mechanisms and future directions

Black carbon (BC) is an important pool of the global C cycle, because it cycles much more slowly than others and may even be managed for C sequestration. Using stable isotope techniques, we investigated the fate of BC applied to a savanna Oxisol in Colombia at rates of 0, 11.6, 23.2 and 116.1 t BC ha -1 , as well as its effect on non-BC soil organic C. During the rainy seasons of 2005 and 2006, soil respiration was measured using soda lime traps, particulate and dissolved organic C (POC and DOC) moving by saturated flow was sampled continuously at 0.15 and 0.3 m, and soil was sampled to 2.0 m. Black C was found below the application depth of 0-0.1 m in the 0.15-0.3 m depth interval, with migration rates of 52.4 ± 14.5, 51.8 ± 18.5 and 378.7 ± 196.9 kg C ha -1 yr -1 (± SE) where 11.6, 23.2 and 116.1 t BC ha -1 , respectively, had been applied. Over 2 years after application, 2.2% of BC applied at 23.2 t BCha -1 was lost by respiration, and an even smaller fraction of 1% was mobilized by percolating water. Carbon from BC moved to a greater extent as DOC than POC. The largest flux of BC from the field (20-53% of applied BC) was not accounted for by our measurements and is assumed to have occurred by surface runoff during intense rain events. Black C caused a 189% increase in aboveground biomass production measured 5 months after application (2.4-4.5 additional dry biomass ha -1 where BC was applied), and this resulted in greater amounts of non-BC being respired, leached and found in soil for the duration of the experiment. These increases can be quantitatively explained by estimates of greater belowground net primary productivity with BC addition.

Fate of soil applied black carbon: downward migration, leaching and soil respiration [Approved article]

Effects and mechanisms of biochar-microbe interactions in soil improvement and pollution remediation: A review.

Biochar amendment improves crop production in problem soils: A review.

After entering the twenty-first century, biochar has become a focal point of multidisciplinary research because of its special characteristics, broad application, and promising development prospects. Basic and applied research on the application of biochar in the areas of agriculture, environment, and energy have increased dramatically in the face of food security, environmental pollution, and energy shortage. Although there are some disputes about biochar research, many studies have demonstrated the importance of biochar research from the perspective of scientific advancement and practical application. This paper briefly recalls the history of biochar application; introduces research progress on the basic characteristics of biochar and its associated production technologies; summarizes the research status and existing problems of biochar application in the areas of agriculture, environment, and energy; and analyzes the potential problems and development trends of biochar research in the future.

Past, present, and future of biochar

Rice husk biochar impacts soil phosphorous availability, phosphatase activities and bacterial community characteristics in three different soil types

Effects of maize stover and its biochar on soil CO2 emissions and labile organic carbon fractions in Northeast China

Biochar as a novel niche for culturing microbial communities in composting.

Biochar is considered difficult for microorganisms to decompose, and volatile organic compounds (VOCs) sorbed to fresh biochar may affect the survival rate of inoculants or the structure of soil microbial communities. We tested the hypotheses that VOCs on fresh biochar may play a vital role in shaping the structure of soil microbial communities and determined if they inhibited or supported the growth of inoculants. We examined the growth of Bacillus mucilaginosus in mushroom medium-based biochar (MM-biochar), corn stalk-based biochar (CS-biochar), and rice straw-based biochar (RS-biochar) in comparison with peat. The composition of VOCs before and after the incubation was characterized by pyrolysis-gas chromatography/mass spectroscopy (GC-MS). The structure of a soil microbial community incubated in biochar was examined via denaturing gradient gel electrophoresis (DGGE). Canonical correspondence analysis (CCA) was applied to reveal the contribution of pH, K and Na, and diversity indices from VOC fingerprints to diversity indices in DGGE profiles. In the present study, all biochars were able to support B. mucilaginosus at population densities analogous to peat. Phenols comprise a fraction of the VOCs that potentially could be toxic to some microbes and inhibit their growth in the short time. The structure of the inoculated soil microbial communities in terms of the diversity indices calculated from 16S ribosomal DNA (16S rDNA) and 18S rDNA DGGE profiles was greatly affected by biochar. Besides, CCA revealed the role of VOCs in shaping the structure of soil microbial communities. VOCs absorbed to biochar, despite their short life spans, could support the survival of B. mucilaginosus, demonstrating the potential of biochars as carriers for inoculants. The changes in the soil microbial communities induced by fresh biochar may not represent the long-term “biochar effect.” Therefore, future work needs to appreciate mechanisms underlying aged biochar on the structure of soil microbial communities.

/pdf/effect-of-volatile-organic-compounds-absorbed-to-fresh-4txhicdiys.pdf

Jun Meng

Papers

Past, present, and future of biochar

Rice husk biochar impacts soil phosphorous availability, phosphatase activities and bacterial community characteristics in three different soil types

Effects of maize stover and its biochar on soil CO2 emissions and labile organic carbon fractions in Northeast China

Biochar as a novel niche for culturing microbial communities in composting.

Effect of volatile organic compounds absorbed to fresh biochar on survival of Bacillus mucilaginosus and structure of soil microbial communities